How do I fix true depth camera, for my Face ID

This is generally a hardware issue. If the unit's on an OS version older than 16.5.1, you might be able to fix it by updating it from a computer or the Software Update function in Settings; otherwise, contact Apple Support.

(241028)

Hello,

Apple has several documents helping you with Face ID.

This document is specific to seeing a 'disabled' Face ID alert, and explains what to do when you see that notice. --> If an alert says Face ID has been disabled on your iPhone or iPad Pro - Apple Support

If you don't see a 'disabled' message but do have general issues with Face ID not working properly, explore the list of things to try in this document: If Face ID isn't working on your iPhone or iPad Pro - Apple Support

If the first 8 don't solve the issue then use #9, contact Apple.